1. Field of the Invention
The present invention relates to a metal gasket raw material plate and, more particularly, to a laminated metal gasket raw material plate in which a rubber layer is provided on a metal plate, and a manufacturing method therefor.
2. Prior Art
Conventionally, as a gasket raw material plate used around an engine mounted on a vehicle etc., a material plate in which asbestos is stiffened by nitrile rubber, phenolic resin, or the like and is laminated has been used. However, because of the recent restriction of asbestos, a laminated metal gasket raw material plate in which a rubber layer is provided on a metal plate via an adhesive layer without the use of asbestos like a rubber coated metal has been used as disclosed in Japanese Patent Application Opened No. H2-38760.
For example, when a gasket is used in a portion in which temperature is changed greatly by repeated operation and stoppage of engine, such as a gasket insertion portion of engine, fretting occurs at the interfaces with engine and gasket due to the temperature change. On the other hand, in particular, a gasket in which a metal plate to which an adhesive is applied is coated with fluororubber, acrylonitrile rubber, etc. to form a rubber layer has high frictional resistance and thus is less liable to slip because the surface of gasket consists of the rubber layer.
For this reason, if a gasket having the surface consists of a rubber layer is used for an engine, a high shearing stress is created by the fretting, and resultantly a peeling phenomenon takes place between the metal plate and the bonding layer. As a result, there arises a problem in that the rubber layer peels off from the metal plate. Also, cooling water (antifreeze liquid containing an electrolyte component), which is one of objects to seal the gasket, may permeate in the surface of metal plate, so that an alkaline substance is formed. By this phenomenon as well, a peeling phenomenon is caused between the metal plate and the bonding layer. As a result, there arises a problem in that the rubber layer peels off from the metal plate.
In order to eliminate the above-described peeling phenomena, conventionally, aqueous solution containing a chromium compound, phosphoric acid, and silica (commercially available coating type chromate treatment agent, for example, trade name Surfcoat NRC300TH manufactured by Nippon Paint Co., Ltd. or trade name Zinchrom R1415 manufactured by Nihon Parkerizing Co., Ltd.) is applied onto the surface of a metal plate such as an aluminum plate, iron plate, and galvanized steel plate etc. by the impregnation method or roll coat method, and is dried to form a composite coating.
However, as environmental problems have become serious in recent years, it has been demanded to make the load to environment as small as possible in the surface treatment of gaskets. In particular, chromate treatment using chromium oxide presents a problem of the discharge of industrial wastes, adverse influence of hexavalent chromium on the environment, or toxic effect on human body. Therefore, it is inevitable for rubber coating to develop a pretreatment technology having little effect on the environment and human body.
An object of the present invention is to provide a non-chromium treated material in which peeling resistance between a metal plate and a rubber layer via a primer layer and a bonding layer, which is decreased by fretting and antifreeze liquid, can be improved, the rubber layer is less liable to peel from the metal plate, and the material has little effect on the environment and human body.
The present invention has been made to advantageously solve the above problems. The invention provides a metal gasket raw material plate of a laminated form in which a rubber layer is provided on a metal plate via a bonding layer, wherein a primer layer of a silica-alumina condensate is formed between the surface of the metal plate and the bonding layer.
For the metal gasket raw material plate in accordance with the present invention, the primer layer of a silica-alumina condensate bonded chemically to the surface of metal plate is formed on the surface of metal plate by a condensation reaction. On the other hand, the silica-alumina condensate of the primer layer is bonded chemically to the bonding layer, and the alumina of the silica-alumina condensate projects from the primer layer to serve as an anchor between the primer layer and the bonding layer, so that the rubber layer is fixed firmly to the metal plate via the primer layer and the bonding layer.
Therefore, according to the metal gasket raw material plate in accordance with the present invention, since the metal plate, primer layer, and bonding layer are bonded chemically to each other, the bond strength can further be increased and the peeling resistance between the metal plate and the rubber layer via the primer layer and the bonding layer can be improved as compared with the conventional chromate treatment agent. Thereby, the rubber layer can be certainly prevented from peeling from the metal plate.
Moreover, according to the metal gasket raw material plate in accordance with the present invention, since chromium oxide is not used in the surface treatment of gasket, the before-mentioned problem of adverse influence on the environment or toxic effect on human body occurring when chromium oxide is used does not arise, and a metal gasket raw material plate having little effect on the environment and human body can be provided.
Further, the invention provides a manufacturing method for a metal gasket raw material plate in which when the primer layer of the metal gasket raw material plate according to the present invention is formed, a mixture produced by mixing aluminum hydroxide with a silane coupling agent at a ratio of 0.5 to 15% by weight of aluminum hydroxide to 5% by weight of solid content in the silane coupling agent is applied onto the surface of the metal plate and is heated.
In the manufacturing method for a metal gasket raw material plate in accordance with the present invention, for example, fine powders of aluminum hydroxide (for example, trade name Higilite H-42M manufactured by Showa Denko K. K.) is added to, for example, an amino silane based or epoxy silane based silane coupling agent (for example, trade name KBM602 or KBM403 manufactured by Shin-Etsu Chemical Co., Ltd. or trade name NUC Silicone Primer APZ-6633 manufactured by Nippon Unicar Co., Ltd.) in a ratio of 0.5 to 15% by weight of aluminum hydroxide to 5% by weight of solid content in the silane coupling agent, and is agitated and dispersed until the mixture becomes homogeneous. Then, the mixture is applied directly onto the surface of a metal plate (for example, a stainless steel plate of SUS301S etc.) formed of an alloy containing chromium, by using, for example, a roll coater, and is heated at a temperature of 250 to 300xc2x0 C. for several minutes. Thereupon, a dehydration condensation reaction takes place, so that hydroxyl group of aluminum hydroxide and hydrogen of the silane coupling agent are bonded chemically to each other, and water is removed therefrom to yield aluminum oxide (alumina). The yielded aluminum oxide projects from the primer layer to serve as an anchor between the primer layer and the bonding layer. On the other hand, between the metal plate and the silane coupling agent, water is removed from the silane coupling agent, so that chromium in the metal plate and the aforementioned aluminum oxide are bonded chemically to each other via silicon contained in silica of the silane coupling agent. Thereby, the primer layer of a silica-alumina condensate bonded chemically to the metal plate is formed on the surface of the metal plate.
Furthermore, for example, a phenol-based or epoxy-based adhesive is applied onto the primer layer by using, for example, a roll coater, and is heated at a temperature of, for example, 250 to 300xc2x0 C. for 0.5 to 5 minutes. Thereby, the primer layer having been bonded chemically to the metal plate and the adhesive having been applied thereto are bonded chemically to each other to form the bonding layer on the primer layer. Then, the rubber layer of, for example, acrylonitrile-butadiene rubber (NBR) based synthetic rubber or the like is provided on the bonding layer.
Therefore, according to the manufacturing method for a metal gasket raw material plate in accordance with the present invention, since the metal plate, primer layer, and bonding layer are bonded chemically to each other, the bond strength can be increased further and the peeling resistance between the metal plate and the rubber layer via the primer layer and the bonding layer can be improved as compared with the metal gasket using the conventional chromate treatment agent. Thereby, the rubber layer can be certainly prevented from peeling from the metal plate.
Moreover, according to the manufacturing method for a metal gasket raw material plate in accordance with the present invention, since chromium oxide is not used in the surface treatment of gasket, the before-mentioned problem of adverse influence on the environment or toxic effect on human body occurring when chromium oxide is used does not arise, and a manufacturing method for a metal gasket raw material plate having little effect on the environment and human body can be provided.
Further, in the manufacturing method for a metal gasket raw material plate in accordance with the present invention, the particle size (particle diameter) of the aluminum hydroxide may be in the range of 0.5 to 5 xcexcm. In this case, the anchoring property between the bonding layer and the primer layer can be kept high and also a smooth primer layer can be formed due to the fine powders of alumina of silica-alumina condensate in the primer layer.
As described above, the particle size of aluminum hydroxide is in the range of 0.5 to 5 xcexcm. The reason for this is that if the particle size of alminum hydroxide is smaller than 0.5 xcexcm, the anchoring property between the primer layer and the bonding layer decreases because the particles of alumina in the silica-alumina condensate formed by the dehydration condensation reaction are too small, and on the other hand, if the particle size of alminum hydroxide is larger than 5 xcexcm, the particles in the primer layer come out onto the surface of the primer layer, so that the primer layer is not smooth.